misc: updated shabang for python script

The default python on MacOS doesn’t have an alias to python2.
The official python version supported in gem5 is Python2.7.

This patch updates the shabang according to the version required in gem5.

Change-Id: I9533c0f7858b5b3cab0ef101be1ee5cd718105b0
Reviewed-on: https://gem5-review.googlesource.com/c/15375
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

tests,style: add RISC-V assembly tests

This patch adds a subset (rv64*) of RISC-V assembly tests. The original
riscv-test project can be found here:
https://github.com/riscv/riscv-tests. The riscv-test project is under the
BSD license (https://github.com/riscv/riscv-tests/blob/master/LICENSE)
and is maintained separately from gem5 project.

The tests have been slightly modified to work in gem5 SE mode:

(1) Removed a trap handler used in riscv-tests for bare-metal systems

(2) Instead of throwing an exception, the tests call the exit syscall
with
the exit code of
- '0' if SUCCESS
- Failed test case's number (non-zero) if FAILURE
The exit code can be captured after a simuation completes.

In addition to original RISC-V assembly tests, this patch adds several
assembly tests specifically for AMO, LR, SC and system calls. Those
tests target a multi-core system.

(1) rv64uamt: multi-threaded tests for A-extension instructions

(2) rv64samt: multi-threaded tests for clone and futex system calls

This patch also makes the style checker ignore RISC-V assembly test
directory. The assembly tests are maintained in an external project
that does not follow the gem5 coding conventions.

Please find more details in the README file included in this patch.

Change-Id: Id1015d9a2c6c7d0341fa8b81483289e5f0bfcec0
Reviewed-on: https://gem5-review.googlesource.com/6703
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

misc: Update #!env calls for python to explicit version

In some newer Linux distributions, env python default to Python 3.0. This
patch explicitly uses "python2" instead of just "python" for all scripts
that use #!

Reported-by: Sanchayan Maity <maitysanchayan@gmail.com>
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>

style: ignore test data in style checks

Change-Id: If797eaf3842b5c1604942bb60f091800ee814a2a
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

style: Refactor the style checker as a Python package

Refactor the style checker into a Python module that can be reused by
command line tools that integrate with git. In particular:

* Create a style package in util
* Move style validators from style.py to the style/validators.py.
* Move style verifiers from style.py to the style/verifiers.py.
* Move utility functions (sort_includes, region handling,
file_types) into the style package
* Move generic code from style.py to style/style.py.

Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Steve Reinhardt <steve.reinhardt@amd.com>